Tag: ESXi

What is SAHF and LAHF and why do I need it to install vSphere 5.1?

Happened to look over the ESXi 5.1 documentation today (yeah, yeah, normally I just install and don’t RTFM) and noticed this in the Hardware Requirements section:

  • ESXi 5.1 will install and run only on servers with 64-bit x86 CPUs
  • ESXi 5.1 requires a host machine with at least two cores
  • ESXi 5.1 supports only LAHF and SAHF CPU instructions
  • ESXi 5.1 requires the NX/XD bit to be enabled for the CPU in the BIOS

Most of the requirements are fairly straightforward, the 64-bit CPU requirement has been there since vSphere 4 was introduced, but many people probably don’t know what NX/XD & LAHF/SAHF are. The NX/XD bit is a CPU feature called Never eXecute, hence the NX name. What the NX bit does is enable the ability to mark certain areas of memory as non-executable with a flag. When this happens the processor will then refuse to execute any code that resides in those areas of memory. Any attempt to execute code from a page that is marked as no execute will result in a memory access violation. This feature adds a layer of security to a computer by providing a protected area against malicious code such as viruses and buffer overflow attacks.

AMD first added the NX bit feature to their AMD64 processor line starting with the Opteron processor starting in 2003. So you may be wondering about the XD part, well that is simply Intel’s name for the same feature which they refer to as eXecute Disable. Intel introduced support for the XD bit shortly after AMD with their Pentium 4 Prescott processor in 2004. Both the NX bit and the XD bit have the exact same functionality just different names so you will often see it as referred to as NX/XD. This feature has been standard on most processors for years now so almost every server built since 2006 should have it. Support for NX/XD is typically enabled or disabled in the server BIOS and is typically found under Processor options and labeled as something like “Execute Disable Bit”, “NX Technology” or “XD Support”.

Many virtualization admins know what NX/XD is but LAHF & SAHF CPU instructions are a processor function that you have probably never heard of. LAHF stands for Load AH from Flags and SAHF stands for Store AH into Flags. LAHF & SAHF are used to load and store instructions for certain status flags. Instructions are basic commands composed of one or more symbols that that are passed to a CPU as input. These instructions related to LAHF & SAHF are used for virtualization and floating-point condition handling. You really don’t need to understand how they work as they are related to the core CPU architecture but if you want to understand them better you can read more about them here.

Support for LAHF and SAHF instructions appeared shortly after NX/XD was introduced. AMD introduced support for the instructions with their Athlon 64, Opteron and Turion 64 revision D processors in March 2005 and Intel introduced support for the instructions with the Pentium 4 G1 stepping in December 2005. So again most most servers built after 2006 should have CPUs that support LAHF/SAHF. Similar to NX/XD which can be enabled or disabled in the server BIOS, support for LAHF/SAHF is typically tied into the Virtualization Technology (VT) option in a server BIOS which is often referred to Intel VT or AMD-V which is their respective support for virtualization CPU technology. The option to enable this on a HP Proliant BIOS is shown below:


So how do you know if your server’s CPUs support NX/XD & LAHF/SAHF? As I said before if you’ve purchased a server in the last 5 or so years, it most likely will support it. If it doesn’t support it the ESXi installer will warn you when you install it as shown below:


Interesting enough though it will still let you install it despite not having the required CPU features. Prior versions of vSphere used to give you an error saying your CPU doesn’t support Long Mode and wouldn’t let you install it. If you do get the error above the first thing to check in that case is if you have those options enabled in the BIOS, if you don’t see those options in the BIOS then your CPU may not support them. You can check your specific CPU’s specifications on Intel’s or AMD‘s websites. You can also check VMware’s Hardware Compatibility List but be aware that there are many processor types/server models not on the HCL that will still work despite not being on the list, they just are not officially supported.

Another way to know if your CPU’s support the required features is to use VMware’s CPU Identification Utility which is a small little ISO that you can boot your host from and it will check the CPU hardware to see if it will support vSphere. I’ve mounted it using the iLO management on server and have also mounted it to a VM’s CD-ROM and booted from it and ran it. Since the CPU hardware is not emulated it can see what type of physical CPU the host is using and what features it supports. The output of the CPU ID tool is shown below, this server fully support all the required CPU features for vSphere:


So there you have it, now you know more about NX/XD & LAHF/SAHF than you probably wanted to know but at least you have an understanding of what they are when you read about the CPU requirements in the vSphere documentation. You probably won’t find any modern servers that don’t support it but often times our data centers become server graveyards and contain a lot of older hardware that keeps getting re-used until they finally die which may not support it. So knowing what to look for when it comes to CPU features is good to know.

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New ESXi 5.0 build to fix Software iSCSI Initiator issue

VMware has recently released a new build of ESXi to fix a bug that causes ESXi to hang for a long period of time while it tries to connect to all iSCSI targets. I’ve personally seen this happen in my lab and it can take quite a long time for ESXi to boot as it will try 9 times to connect to each iSCSI target. VMware sees this as a serious enough issue that not only have they released a patch to fix the problem but they’ve also released a special patch express release of ESXi. So when you go to download ESXi 5.0 now you will see two options for the ESXi ISO: one for systems without software iSCSI configured and one for systems with software iSCSI configured. If you are already using software iSCSI or plan on it at some point  you should choose the ISO image for systems with software iSCSI. You can read more about this issue in this VMware KB article. Here is the details on the two ESXi builds:

  • Original release: Version 5.0.0 – Release Date 8/24/11 – Build 469512
  • iSCSI patch release: Version 5.0.0 – Release Date 11/10/11 – Build 504890


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Patching VMware ESXi Installable

ESXi 4.1 brought changes to the patching process. Previously, the Host Update utility — an application included with the vSphere Client — could patch ESXi 4.0 hosts. VMware removed Host Update from ESXi 4.1, presumably to encourage users to upgrade to paid versions that are managed and patched with vCenter Server’s Update Manager. As a result, the only method left to patch the free version of ESXi is with the vihostupdate command-line utility, which is included in the vSphere Command-Line Interface (CLI).

Before using this method, it’s important to understand how the patches work and where to find them.

Read the full article at searchvmware.com…

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Installing and configuring VMware ESXi

VMware announced that ESXi will be the exclusive hypervisor of vSphere 5. As such, we will likely see a greater adoption of VMware’s smaller hypervisor.

ESXi can be either embedded on a server (boot from flash) or installed on existing servers, using the Installable version. The free version of ESXi, the VMware vSphere Hypervisor, includes support for virtual symmetric multiprocessing (vSMP) and thin provisioning. No additional features are included, which means the free version of ESXi cannot be managed by vCenter Server, because it does not include a vCenter Server agent. To gain additional features and a vCenter Server agent, you need to upgrade your ESXi license.

The ESXi installation uses about 5 GB of space. Any remaining space on the drive is automatically formatted as a Virtual Machine File System (VMFS) partition. The hypervisor needs roughly 32 MB; the additional space is used for VMware Tools as well as swap and core dump partitions.

If you already have existing licenses for ESX, you can also choose to deploy ESXi in place of ESX on a server. Simply download ESXi installable. Install it and then license it with vCenter Server, as you would a traditional ESX server. Follow the steps below to install and configure ESXi.

Read the full article at searchvmware.com…

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ESX vs. ESXi: Convincing your boss to move to ESXi

Since VMware first introduced its ESXi hypervisor at the end of 2007, the ESX-vs.-ESXi debate has escalated. But now that VMware plans to phase out ESX and switch to ESXi, migrating to ESXi has become increasingly important.

But the reality is that many VMware shops still run the ESX hypervisor. ESXi has a radically different management approach, and many ESX shops have avoided ESXi because it lacked the power of ESX’s service console. Additionally, several ESX features were not available in early ESXi iterations.

But ESXi has steadily matured, and now the consensus is that the stripped-down hypervisor is on par with ESX’s features and management. But many IT shops still run ESX because they are used to it, and the transition to ESXi can be time-consuming and difficult.

Now that ESXi will replace ESX, you may be ready to switch hypervisors. But you might have to convince your boss and coworkers to get on board. To end the ESX vs. ESXi debate for good, this sample letter should help you make a convincing argument for migrating to ESXi.

Read the full article at searchvmware.com…

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Upgrading hosts from ESX to ESXi in seven steps

The next release of vSphere won’t include VMware ESX, so you may be unsure how to upgrade your ESX hosts to ESXi hosts. Unfortunately there is no magic bullet, and as with all upgrades, you should not rush into it without being prepared. In this article, I will provide a suggested methodology.

1. Understand the differences between ESX and ESXi

First, you need a good understanding of the differences between ESX and ESXi. The two hypervisors run the same VMkernel, but managing ESXi is different from management ESX. ( VMware provides a basic ESX vs. ESXi comparison on its website and a more detailed one in the ESX vs. ESXi 4.1 KnowledgeBase article.) ESX and ESXi used to differ considerably, but vSphere 4.1 addressed most of them and the two hypervisors are now on par with each other.

Read the full article at searchvmware.com…

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Test ESXi 4.1 today, migrate smoothly from ESX tomorrow

VMware has long claimed that ESXi will one day be the Palo Alto-based company’s main hypervisor, and the time has come for ESX to begin to gracefully make its exit. The recent release of VMware vSphere 4.1 will be the last release to include the ESX version of VMware’s hypervisor, which may not make ESX fanboys happy. The improvements in ESX 4.1, however, demonstrate that the time to start switching is now.

In a recent Virtualization Viewpoints column, I wrote about drawbacks of VMware ESXi and why widespread adoption of ESXi is not a reality. Some of the problems with ESXi included:

  • No official support for booting ESXi from a storage area network (SAN),
  • no Web-based console to manage virtual machines (VMs),
  • no support for scriptable installations, and
  • no support for Active Directory (AD) integration.

The article also outlined several suggestions for making ESXi more attractive to administrators used to working with ESX. While I have always preferred ESX over ESXi, I am now recommending that you start using ESXi and plan on migrating all of your current ESX installations to the ESXi platform.

Read the full article at searchvmware.com…

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ESXi Links

PXE Booting VMware ESXi (VMware)
ESXi 4 Quick Install Guide (Xtravirt)
ESX3i to ESX4i Update (Technodrone)
Upgrade ESXi 3.x to 4.0 Video (VMware Tips)
Installing VMware ESXi 4.0 on a USB Memory Stick – The Official Way (TechHead)
vSphere ESXi on a USB memory stick (Yellow Bricks)
Three ways to kill a frozen vSphere ESXi host virtual machine (Virtualization Pro)
How-to install ESXi 4.0 on USB memory Key (ESX Virtualization)
Create ESXi 4 USB flash drives with Workstation (vCritical)
The Mechanics of VMware GO (SearchVMware.com)
Using VMware Go to get going on your ESXi virtualization project (SearchVMware.com)
Using ESXi & VMware Go – Part 1 Download & Install (Professional VMware)
VIDEO: Jumpstart ESXi and P2V with VMware GO (VMware Videos)
ESXi Lessons Learned – Part 1 (Yellow Bricks)
ESXi Lessons Learned – Part 2 (Yellow Bricks)
VMware Easter Egg? Easy Install of ESXi 4 On VMware Player 3.0 (VM/ETC)
VMWare ESXi 4.0 Installation on UCS Blade Server with UCS Manager KVM (Cisco)
10 Reasons why VMware ESXi 4 is perfect for the SMB (Virtualization Admin)
10 Steps to Install and Use the Free VMware ESXi 4 (Virtualization Admin)
Restarting the Management agents on an ESX or ESXi Server (VMware KB)

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